This invention is in the field of salt recovery by means of solution mining. More particularly, it involves an improved method of connecting wells for salt production where a greater proportion of the salt present in the formation can be recovered efficiently.
The original method of producing salt by solution mining was to drill a vertical hole from the surface into the salt bed, pump fresh water in through the casing annulus, contacting the fresh water against the salt along the walls of a cavity formed at the base of the well and discharge brine up the tubing to the surface.
Another known method is to drill two spaced apart conventional vertical wells into a salt formation. Solution mining is employed in each well, creating cavities. Oil is introduced into each cavity which forms a nonsoluble pad in the upper surface of each cavity. This causes the cavities to form more rapidly in horizontal directions. The flattened cavities grow in size until they coalesce, that is, join together, at which time the formation can be mined by pumping fresh water into one well and removing brine from the other. This method has the disadvantage that both wells must be completed for individual mining operation and the process to achieve coalescence is slow.
Still another method is to drill two conventional vertical wells spaced apart from each other. One or both of the wells are fractured by high pressure by the known procedure frequently employed by the petroleum industry. If the fracture operation opens up a flow passageway between the two wells, water can then be pumped down one well and brine removed from the other. The problem with this method is that there is no way to control the direction of fracture. Therefore, to have a good degree of success the wells must be drilled closer together. If the wells are drilled close enough together to insure connection by fracturing, the resulting cavity formation is small and the total salt recovery reduced.